Mapping relational data to RDF is an important task for the
development of the Semantic Web. To this end, the W3C has recently
released a Recommendation for the so-called direct mapping of
relational data to RDF. In this work, we propose an enrichment of
the direct mapping to make it more faithful by transferring also
semantic information present in the relational schema from the
relational world to the RDF world. For this purpose we enrich
DL-LiteRDFS with expressive identification constraints to capture
functional dependencies and define an RDF Normal Form, which
precisely captures the classical Boyce-Codd Normal Form of
relational schemas.